Bell Labs

About: Bell Labs is a based out in . It is known for research contribution in the topics: Laser & Optical fiber. The organization has 36499 authors who have published 59862 publications receiving 3190823 citations. The organization is also known as: Bell Laboratories & AT&T Bell Laboratories.

Model checking and abstraction

Abstract: We describe a method for using abstraction to reduce the complexity of temporal-logic model checking. Using techniques similar to those involved in abstract interpretation, we construct an abstract model of a program without ever examining the corresponding unabstracted model. We show how this abstract model can be used to verify properties of the original program. We have implemented a system based on these techniques, and we demonstrate their practicality using a number of examples, including a program representing a pipelined ALU circuit with over 101300 states.

Ionicity of the Chemical Bond in Crystals

Abstract: The nature of the chemical bond in crystals is discussed. The general theories of L. Pauling based on thermochemical data and of C. A. Coulson based on valence bond concepts are compared with a recent spectroscopic theory. Particular emphasis is placed on binary crystals of formula ${\mathrm{A}}^{N}{\mathrm{B}}^{8\ensuremath{-}N}$ which includes most tetrahedrally coordinated semiconductors as well as crystals of the rocksalt (NaCl) family. A wide range of physical properties is discussed, including crystal structure, energy bands, elastic constants, ionization energies, and impurity states. The role of quantum-mechanical sum rules and spectral moments in constructing simplified models of bond and band behavior is explored. Stress is laid throughout on methods for incorporating quantum-mechanical effects into properties of chemical bonds through algebraic relations rather than through variational solutions of the wave equation.

Image coding based on a fractal theory of iterated contractive image transformations

Abstract: The author proposes an independent and novel approach to image coding, based on a fractal theory of iterated transformations. The main characteristics of this approach are that (i) it relies on the assumption that image redundancy can be efficiently exploited through self-transformability on a block-wise basis, and (ii) it approximates an original image by a fractal image. The author refers to the approach as fractal block coding. The coding-decoding system is based on the construction, for an original image to encode, of a specific image transformation-a fractal code-which, when iterated on any initial image, produces a sequence of images that converges to a fractal approximation of the original. It is shown how to design such a system for the coding of monochrome digital images at rates in the range of 0.5-1.0 b/pixel. The fractal block coder has performance comparable to state-of-the-art vector quantizers. >

A Method for Comparing Two Hierarchical Clusterings

Abstract: This article concerns the derivation and use of a measure of similarity between two hierarchical clusterings. The measure, Bk , is derived from the matching matrix, [mij ], formed by cutting the two hierarchical trees and counting the number of matching entries in the k clusters in each tree. The mean and variance of Bk are determined under the assumption that the margins of [mij ] are fixed. Thus, Bk represents a collection of measures for k = 2, …, n – 1. (k, Bk ) plots are found to be useful in portraying the similarity of two clusterings. Bk is compared to other measures of similarity proposed respectively by Baker (1974) and Rand (1971). The use of (k, Bk ) plots for studying clustering methods is explored by a series of Monte Carlo sampling experiments. An example of the use of (k, Bk ) on real data is given.